[mythtv-users] Way OT: Re: Power outages and UPSs

[David Brodbeck]

On Jul 30, 2007, at 3:51 PM, f-myth-users at media.mit.edu wrote:
> P.S.  Don't overlook the possibility that your house is poorly
> grounded, especially in a lightning-prone area.

Having done a little reading about what it takes to make a good, low- 
impedance lightning ground, I suspect *most* homes are poorly  
grounded.  A cold water pipe or single ground rod doesn't even begin  
to cut it.  Ideally you'd have at least three rods, all at least six  
feet long and wired in a star configuration.  All the house grounds  
should be bonded to the same point to ensure that everything will  
stay at the same potential in the event of a lightning strike.  I  
seem to recall the ARRL Handbook had a good section on earth  
grounds.  (It's an important topic for radio amateurs, both for  
lightning protection and antenna efficiency reasons.)

MythTV content: Poor grounding is also a common source of cable TV  
signal problems.  When the power and cable grounds are not the same,  
ground loops are introduced that create interference.  I often see  
cable TV drops grounded to a puny piece of 3/8" rod hammered into the  
dirt.

The NEC grounding standards are aimed mostly at protecting your life  
by ensuring a proper return path for faults, and won't necessarily  
protect equipment from damage.